Mass, Gas and Galaxies in the Abell 901/902 Supercluster

Mass, Gas and Galaxies in the Abell 

901/902 Supercluster 

Catherine Heymans 

on behalf of the STAGES collaboration 

(PI: Meghan Gray) 

University of British Columbia, Vancouver. 

Canadian Institute for Theoretical Astrophysics, Toronto. 

Institute d’Astrophysique de Paris.

STAGES 

• 80 orbit mosaic 

• ACS + WFPC2/NIC3 

parallels 

• science exploitation 

underway 

• second largest HST 

mosaic 

• sister survey to GEMS/ 

CDFS 

• Data public 20th Feb 

2008! 

Nottingham 

M Gray (PI) 

K Lane 

A Aragón-Salamanca 

O Almaini 

I Trujillo 

Edinburgh 

D Bacon 

A Taylor 

Oxford 

C Wolf 

Innsbruck 

M Barden 

E van Kampen 

image: COMBO-17 

Collaborators 

Texas 

S Joghee 

J Caldwell 

F Barazza 

HIA 

Victoria 

C Peng 

UBC 

C Heymans 

L Van Waerbeke 

Arizona 

C Papovitch 

MPIA Heidelberg 

HW Rix 

E Bell 

K Meisenheimer 

R Somerville 

S Koposov 

K Jahnke 

B Häußler 

X Zheng 

A Pasquali 

UMass 

D McIntosh 

Columbia 

B Johnson 

AIP Postdam 

L Witozski 

A Boehm 

CAHA 

S Sanchez 

ESO/Chile 

R Gilmour 

Waterloo 

M Balogh

Catherine Heymans LBL 22nd Jan 2008

Outline 

✴ The STAGES survey 

• Galaxy evolution in dense environments 

✴ “Seeing the invisible”: mapping the dark 

matter environment of Abell 901/902 

• Weak gravitational lensing 

✴ First galaxy evolution results from the Abell 

901/902 laboratory 


The Abell 901/902 Supercluster 

30x30 arcmin image of the A901/2 supercluster at z=0.165 


A901a 

A901b 

A902 SW group 

Catherine Heymans Ground-based images from COMBO-17 

LBL 22nd Jan 2008

QE (%) 

λ / nm 

COMBO-17 

Wolf et al 2004 

σz ∼ 0.02(1 + z) 

✴ 5 broad band + 12 

narrow band filters 

✴ Photometric redshifts to 

R

STAGES: Space Telescope A901/902 Galaxy Evolution Survey 

Hubble Space Telescope 

(M.E Gray) 

COMBO-17 survey 

(C. Wolf) 

Omega2000 @ Calar Alto 

(K. Meisenheimer) 

2dF spectrograph 

(M. E. Gray) 

XMM-Newton 

(R. Gilmour) 

Spitzer 

(E. F. Bell) 

GALEX 

(GALEX team) 

GMRT 

(D. Green) 

constrained simulations 

(E. van Kampen) 

80 orbit mosaic; ACS, NICMOS, WFPC 

morphologies, weak gravitational lensing 

17-band optical imaging: 

photo-zs + SEDs for 15000 objects 

near-infrared extension (Y, J1, J2, H): 

M*, photo-zs 

spectroscopy of ~300 cluster galaxies: 

dynamics, star-formation histories 

90 ks X-ray imaging/spectroscopy: 

ICM, AGN 

infrared imaging (8 and 24 µm): 

obscured star formation, AGN 

NUV + FUV imaging: 

unobscured star formation 

radio imaging (610 and 1400MHz) 

obscured SF, AGN 

N-body + hydro + semi-analytic models 

dark matter, gas, galaxies 


Massive ellipticals live 

in cluster cores 

What physical mechanism drives galaxy 

evolution in dense environments? 

Spirals, typically live in the 

outskirts of the supercluster 


LSB galaxy 

1: Galaxy-cluster gravitational interations: 

Zoom in: Side on view Zoom in: Face on view 

Galaxy Harassment movie: The evolution of a low surface 

brightness galaxy as it falls into a cluster (Moore et al 1998) 


Ram pressure 

stripping: The 

turbulent history of a 

spiral galaxy as it falls 

through the hot ICM 

of a rich galaxy 

cluster (Quilis et al). 

2: Galaxy-cluster gas interations: 


3: Galaxy-cluster galaxy interations: 

Galaxy Merger movie (Dubinski et al) 


1. Galaxy-cluster gas interactions 

• ram-pressure stripping 

2. Galaxy-cluster gravitational interactions 

• tidal truncation of galaxy dark matter halos 

3. Galaxy-galaxy interactions 

What physical mechanism drives galaxy 

evolution in dense environments? 

• mergers (low-speed interactions) 

• galaxy harrassment (high-speed 

interactions) 

Any hope of disentangling 

these effects requires 

knowledge of the 

environment; in terms of 

mass, gas and galaxies. 


Dark Matter is the underlying structure of the Universe, 

dictating where and when galaxies form. 

Meghan Gray (University of Nottingham) The Millennium and Catherine Heymans simulation: (University Max of British Planck Columbia) Institute

Seeing the invisible 

Meghan Gray (University of Nottingham) and Catherine Heymans (University of British Columbia)

Seeing the invisible 


lensed background 

galaxy z = 1.55 

lens galaxy z = 0.168 

Aragon-Salamanca et al in prep 


The dark matter signature on the sky 

Matter 

Distant galaxies Dark Matter 

We can use the ‘lensing’ signature of dark matter 

to tell us where is it and how much if it there is. 


Tangential arclets in A901a 

In the cores you can see the effect by eye. 


How to make a dark matter map 

1. Obtain deep high resolution imaging. 

2. Measure the ellipticities of distant 

galaxies. 

3. Account for all artifical sources of 

shear (eg instrumental distortions) 

that are typically more than an order 

of magnitude larger than the signal 

you’re trying to detect (see STEP). 

4. Directly from GR you can relate the 

measured shear to the projected mass. 

ACS PSF 

e i =e i source + γi 

= 0 γ ≈ 



In this analysis we use 60,000 

galaxies that are behind the 

supercluster (65 gals per sq 

arcmin) to reconstruct the dark 

matter distribution 

A901b 

A902 SW group 


LBL 22nd Jan 2008

130kpc resolution at supercluster redshift z=0.165 

Heymans et al 2008 

from 80 orbits of HST 

Catherine Heymans LBL 22nd Jan 2008 

κ 

Contours show 

detections 

2σ, 4σ, 6σ

What about systematics? 

B 

E 

Lensing only produces 

Emode distortions 

: systematics 


κ

M = 6.1 ± 0.8h −1 10 13 M⊙ 

M/L = 131 ± 16hM⊙/L⊙ 

M/M∗ = 32 ± 4 

ACS HST image 


Infalling X-ray 

group A901α 

Dark Matter density 


A901b: the most 

massive and X-ray 

rich of the four 

clusters 

Dark Matter 

map resolves 

substructure 

M = 6.5 ± 1.3h −1 10 13 M⊙ 

M/L = 165 ± 33hM⊙/L⊙ 

M/M∗ = 42 ± 8 

ACS HST image Dark Matter density 


A902 has two peaks in the 

dark matter distribution 

that are matched by two 

BCGs 

CBI z=0.46 

M = 3.3 ± 0.8h −1 10 13 M⊙ 

M/L = 108 ± 25hM⊙/L⊙ 

M/M∗ = 28 ± 6 



SW group 

M = 3.8 ± 0.5h −1 10 13 M⊙ 

M/L = 176 ± 24hM⊙/L⊙ 

M/M∗ = 41 ± 6 



Mass and Light 

M/L ∼ 100h −1 M⊙/L⊙ 


Mass to stellar mass ratio 


Ground based Map from 

Gray et al 2002 

Why HST? 


κ 

Future space-based missions such as 

SNAP and DUNE are going to be vital 

for future dark matter observations 

κ

Why Hubble? ground-based 


Why Hubble? 

STAGES 

answer: image quality and resolution allows us to detect the weak dark matter signature 


Future telescopes in space: a 

quick note about depth 

✴ It’s not just about image quality. 

✴ For high resolution dark matter 

maps, you need depth 

γ ≈ 

✴ A smaller class telescope such as 

DUNE will need to observe much 

longer than SNAP to obtain deep 

enough data for simlarly high 

resolution observations 

DUNE ~ 1.2m 

SNAP ~2m 



STAGES: 

Space Telescope A901/902 Galaxy Evolution Survey 

✴ The lensing map is one key piece of a bigger puzzle 

✴ The larger picture looks at the link between galaxies 

and environment: nature vs nurture? 

✴ Looking at the A901/902 with multi-wavelength eyes 

we have assembled an ideal laboratory for studying 

galaxy evolution 

✴ We are finding that it is the outskirts of the cluster 

where galaxy transformations are occurring 


galaxies 

dark 

matter 

STAGES: a laboratory for studying galaxy 

evolution and environment 

“environment” 

hot 

gas 

• harrassment 

• strangulation 

• stripping 

• tidal truncation 

• merging 

• … 

star 

formation 

“galaxies” 

shapes 

active 

galactic 

nuclei 

sizes 

We need multiwavelength observations in order to get a full census of the supercluster.

Anatomy of a supercluster: 

a complex environment 

Mass 

gravitational lensing: 

Heymans et al 2008 

Gas 

X-ray imaging: 

Gilmour et al 2007 

Step 1: map out the environment 

Galaxies 

optical imaging 

Wolf et al 2004

Mass, Gas and Galaxies 


LBL 22nd Jan 2008

hidden supermassive black hole 

Step 2: understand the galaxies 

XMM GALEX HST Spitzer GMRT 

merging galaxy 

X-ray ultraviolet optical infrared 

radio 

dust obscuration

Galaxy Classification 

E B-V (dust) 

Wolf, Gray & 

Meisenheimer 2005 

Blue Galaxies 

Old Red 


age [Myr] 

Dusty Red 


A population of dusty red star forming galaxies 

make up 30% of the cluster red sequence 

A large population of anemic 

spirals/dusty red galaxies 

Lane et al 2007 

early-type late-type 


Blue 


Step 3: connect galaxies and environment 

Dark 

matter 

contours 

Old Red 


Dusty Red 



Step 3: connect galaxies and environment 

Result: 

it is the intermediate 

density or infall regions 

where most of the 

signatures of galaxy 

transformation are seen. 

Heiderman et al in prep 


What causes galaxy evolution in dense 

✴ It’s not the gas 

environments? 

Preliminary conclusions: 

✴ It’s not high galaxy densities 

✴ The action seems to be where galaxies are first 

experiencing the pull of dark matter 

✴ Our first findings are showing a sweet-spot where 

galaxies become close enough, and are moving slow 

enough to interact and transform. 


Summary 

✴ STAGES is a multi-wavelength survey of the Abell 901/902 

supercluster. 

✴ The survey aims to distinguish between the different physical 

mechanisms which drive galaxy evolution in dense environments. 

✴ Weak lensing analysis of HST images permits high resolution 

dark matter “observations”. 

✴ Old Red Galaxies trace the underlying dark matter distribution 

✴ Intermediate density regions key site for galaxy transformations 

✴ Current work bringing together all different multi-wavelength 

cluster information to form a coherent understanding of the 

violent history of this supercluster

Mass, Gas and Galaxies in the Abell 901/902 Supercluster

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